baresip

baresip for Android is a SIP user agent: it registers with a SIP account, places and receives calls, and exchanges messages over the same protocol. The application is a front end for the baresip library, so the underlying signalling and media handling come from that codebase while the Android layer supplies the dialler, contact handling, and account configuration.

Because it speaks SIP rather than a proprietary protocol, it works against whatever SIP service or PBX you already have credentials for, including self-hosted setups. Alongside SIP telephony, the app covers mobile calling and messaging, which suits people who want one client for both an internet telephony account and ordinary conversations on a handset.

It is published for Android by Juha Heinanen under the BSD-3-Clause licence. There is no desktop build in this listing, though the baresip library it builds on exists independently of the Android packaging.